Preferably, the invention is used in image-assisted navigation (image-guided surgery or IGS). Attaching marker devices to a body structure—for example, a reference star to a bone—and attaching a marker device to a cutting block allows a cutting block to be navigated relative to the body structure and thus allows the cutting block to be positioned exactly relative to the body structure, at a planned location. In order to position the cutting block exactly, an adjusting mechanism is used which is likewise fixed to the bone. In accordance with the prior art, one adjusting mechanism for each cutting block is fixed to the body structure.